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Ammonium transport in mouse colon: Role of NKCC1 and Rh glycoproteins
Author(s) -
Worrell Roger T.,
Engevik Melinda A.
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.796.40
Subject(s) - secretion , chemistry , cell culture , distal colon , microbiology and biotechnology , biology , biochemistry , endocrinology , genetics
We have previously shown that NH 4 + secretion occurs in the colonic crypt cell line, T84 (AJP 294:G429, 2008). In T84 cells, the secretory vector exceeds the absorptive vector thereby resulting in net NH 4 + secretion. This study sought to extend the colonic cell line work to mouse colon. Absorptive NH 4 + flux in isolated mouse distal colon (J ms ) was 80±22 while secretory flux (J sm ) was 404±47, resulting in a net secretory NH 4 + flux of 325±35 μg/cm 2 /hr. As was found in T84 cells, both NKCC1 and RhBG were implicated in contributing to this net secretion. Portal vein [NH 4 + ] was ~1.5 fold higher in NKCC1 −/− and ~1.24 fold higher in NKCC1 +/− mice compared to WT mice indicative of decreased intestinal NH 4 + secretion. Interestingly systemic blood [NH 4 + ] was elevated ~2 fold in the NKCC1 −/− mice suggesting a role for NKCC1 in hepatocyte NH 4 + uptake. By real‐time RT‐PCR, both T84 cells and mouse colon express the ammonium transporters, RhBG and RhCG. Whereas both are expressed equally in T84 cells, the ratio of RhBG to RhCG varied along the length of the colon, with RhBG/RhCG being 9 in proximal colon and 2 in distal colon. RhBG levels were ~1.7 fold higher in NKCC1 −/− verses WT colon yet RhCG levels were unchanged thus supporting a role for RhBG in colonic NH 4 + secretion. These data support the ability of colonic epithelia to actively extrude NH 4 + thereby limiting the interstitial accumulation of this toxic substance. Supported by NIH DK079979.